N-linked protein glycosylation is the most common eukaryotic protein modification and many diseases including autoimmune disorders and cancer are associated with compositional changes of N-glycans. A broad spectrum of N-glycans are specifically recognized by cell surface receptors, and these interactions likely play a critical role in these diseases. The long-term goals of this research are to explore the structure and dynamics of N-glycans as attached to a protein and as specifically coordinated in a protein-protein interaction. Rheumatoid arthritis (RA), an autoimmune disorder, is a crippling disease that can strike at any age, disabling and disfiguring its victims by destroying joint tissue. A recent link between RA and a specific posttranslationally modified form of immunoglobulin G (IgG) provides an important key to understanding the disease and finding a more effective treatment. The modification involves terminal sialylation of the biantennary N-glycans attached to the Fc fragment of IgG. This specific modification is found to dramatically increase the anti-inflammatory activity of IgG, suggesting molecular mimics of the sialylated Fc glycans may be a promising new treatment for RA. The aims of this proposal are: 1) To study the molecular character of terminal sialic acid residues and the effect of sialylation on the N-glycans associated with the Fc fragment of IgG using nuclear magnetic resonance (NMR)-based techniques;2) To develop techniques for the assignment of N-linked glycan resonances. This will utilize the 13C-labeling strategy of Aim 1 combined with a novel mass spectral analysis technique to correlate resonances with either the alpha1-3 or alpha1-6 branch of these complex-type N-glycans;3) To calculate a structure and evaluate the dynamics of the sialic acid-galactose disaccharides at the termini of the N-glycan;and 4) To measure the interaction of the sialylated Fc fragment with its proposed receptor, dendritic cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN). PUBLIC HEALTH RELEVANCE: Rheumatoid arthritis is a debilitating disease that limits the health and productivity of affected individuals. This proposal will utilize recent scientific discoveries to study the details of molecular interactions underlying rheumatoid arthritis. This knowledge will guide the future development of more effective treatments of rheumatoid arthritis.